Retardation and mobilization of arsenic at redox fronts under advective flow conditions - a concerted multidisciplinary approach (AdvectAs)
Final Report Abstract
Elevated levels of arsenic (As) in groundwater are a health problem affecting over 100 million people worldwide, particularly in the densely populated river deltas of South and Southeast Asia. Within the AdvectAs project the role of redox transition zones in delta sediments, which separates low and high As groundwater bodies, were studied for the first time in a multidisciplinary approach. The results of our investigations clearly show that the stability and persistence of redox transition zones in space and time is largely controlled by the mutual interaction of (a) solute transport, (b) microbial activity and (c) the stability of Fe-phases hosting As. Advective flow conditions exacerbate the inflow of organic matter, mainly from fresh riverbank sediments and organic matter intercalations, into the delta aquifer, promoting As release. During the groundwater transport, microbiologically driven redox processes are involved at various stages in As(im)mobilization. Our results point to the fact that methanogenesis is a key process for As mobilization. On the one hand, the gas production affects the groundwater flow, on the other hand, the methanogenesis leads to a dissolution of Fe(III)phases releasing As into the groundwater. The reduced high-As groundwater reaches low-As aquifers by crossing the redox front. These redox transition zones can be recognized macroscopically by color changes (orange/brown and grey) that develop along sedimentological gradients (mainly grain size). Those fronts are relatively narrow in the millimeter range and show a pronounced fingering of several centimeter. Along these narrow transition zones, a certain sequence of Fe minerals could be identified, which are able to fix As in various quantities. Various transformations of Fe phases within this front control the mobilization and retardation of As to a large extent. Age determination of groundwater and modelling results suggest that these redox zones are very stationary and decisive for As retardation. This is a promising result, because the As contaminated groundwater is hindered from propagating further. Surprises: Within the redox transition zone, oscillating redox processes lead to a repeated reduction and oxidation of iron phases, which results in a complex transformation sequence of Fe phases and multiple stages of As release and fixation. - Redox front seems to be very stationary, at least for a period of decades. - In addition to in-situ organic matter, our data suggests that methane plays a key role as electron donor for Fe(III) mineral reduction and arsenic mobilization. Wie giftiges Arsen ins Grundwasser Vietnam gelangt? https://uni-tuebingen.de/university/news-and-publications/newsfullview-news/article/wie-giftigesarsen-ins-grundwasser-vietnams-gelangt/ Tödliche Gefahr: Arsen im Reisfeld https://uni-tuebingen.de/universitaet/aktuelles-und-publikationen/veroeffentlichungen/attempto/ EurasiaReview, https://www.eurasiareview.com/08042020-river-groundwater-hot-spot-for-arsenic ScienceDaily, https://www.sciencedaily.com/releases/2020/04/200407164953.htm EurekAlert, https://www.eurekalert.org/pub_releases/2020-04/fu-rhs040620.php Nature Ecology & Evolution, https://natureecoevocommunity.nature.com/posts/65637
Publications
- (2020). Process-based modeling of arsenic(III) oxidation by manganese oxides under circumneutral pH conditions. Water Research, 185, 116195
Rathi, B., Jamieson, J., Sun, J., Siade, A. J., Zhu, M., Cirpka, O. A., & Prommer, H.
(See online at https://doi.org/10.1016/j.watres.2020.116195) - (2020): Role of in-situ natural organic matter in mobilizing As during microbial reduction of Fe(III)-mineral-bearing aquifer sediments from Hanoi (Vietnam). Environmental Science and Technology 54, 7, 4149-4159
Glodowska M., Stopelli E., Schneider M., Lightfoot A., Rathi B., Straub D., Patzner M., Duyen V.T., Berg M., Kleindienst S., Kappler A.
(See online at https://doi.org/10.1021/acs.est.9b07183) - (2020): Spatial and temporal evolution of groundwater arsenic contamination in the Red River delta, Vietnam: Interplay of mobilisation and retardation processes. Science of the Total Environment 717
Stopelli E., Vu T. D., Tran T. M., Pham T. K.T., Pham H. V., Lightfoot A., Kipfer R., Schneider M., Eiche E., Kontny A., Neumann T., Glodowska M., Patzner M., Kappler A., Kleindienst S., Rathi B., Cirpka O., Bostick B., Prommer H., Winkel L. H. E., Berg M.
(See online at https://doi.org/10.1016/j.scitotenv.2020.137143) - (2020): The river-groundwater interface as a hotspot for arsenic release. Nature Geoscience 13, 288–295
Wallis I., Prommer H., Berg M., Siade A.J., Sun J., Kipfer R.
(See online at https://doi.org/10.1038/s41561-020-0557-6)
